Slipstreaming as a Way of Saving Fuel

Contents

CHAPTER ONE
Concept of Slip Streaming
Applications of Slipstreaming In Real Life

CHAPTER TWO
Basic Definitions related to slipstreaming
Proposal for Slipstreaming Effect Investigation

CHAPTER THREE
The End:
References:
Bibliographies:

“Bismillahir Rahmanir Rahim”

Assalamu alaikum,at first the author expresses his gratefulness to almighty Allah for his mercy and kindness towards him (author)

The author expresses his deep sense of gratitude, regard and sincere thanks to Dr. Mohammad Mashud, Professor of the Department of Mechanical Engineering of Khulna University of Engineering & Technology (KUET), for his magnanimous guidance and valuable counsel in execution and completion of the work

The author also wants to express his gratitude, regard and sincere thanks to Prof. Dr. Muhammed Alamgir, vice chancellor of Khulna University of Engineering & Technology for creating a research friendly environment and recent developments in Khulna University of Engineering & Technology (KUET), Bangladesh

Thanks are also extended to all the teachers of the Department and foreman and staffs of Aerodynamics Laboratory, Machine Shop, Central Computer Center and Central Library of KUET

Author

Abstract

This book focuses on the slipstreaming effect between cars, trailing each other on highways. Slipstreaming is effective at higher velocities of the vehicles under consideration. From various investigations around the world it has already been shown that slip streaming effect is effective on high speeds of vehicles while running on highways. So slip streaming effect can be utilized by the drivers of different cars for saving power of their cars. Which in turn reduces the fuel consumption. Because the more power the more fuel is needed. As the fuel consumption of the vehicle reduces it will in turn reduces the overall driving cost

CHAPTER ONE

Concept of Slip Streaming

Drag is the force that opposes a car's motion through the air. Drag is produced by every part of the vehicles. Drag is a mechanical force. It is generated by the interaction and contact of a solid body with a fluid (liquid or gas). It is not generated by a force field, in the sense of a gravitational field or an electromagnetic field. In gravitational field or an electromagnetic field one object can affect another object without being in actual or real contact. For drag to be produced, the solid body must be in contact with the fluid. Reduction of drag has always been the concern of any aerodynamic design. As far as ground vehicles are concerned, 90% of the overall drag is contributed by the pressure differences in front and rear end of the vehicle which is called pressure drag. This is due to the separation of flow at the trailing edge of the vehicle are due to turbulence and vortices. This produces a low pressure turbulent region behind the vehicle, called wake. As the vehicle moves forward the wake also moves with it. The movement of air behind the vehicle is termed as slipstream. Many methods have been developed to reduce this pressure drag. Spoilers can be used to reduce the pressure drag but it adds to the skin friction drag hence reduction in overall drag is not appreciable ^[1].The utilization of the slipstream of a leading vehicle and hence reducing the drag of trailing vehicle is termed as slipstreaming. Slipstreaming was first observed among birds. Group of birds flying in a specific pattern reduces their overall drag force. The bird leading will experience more drag and hence needs more effort than trailing birds ^[2].

Applications of Slipstreaming In Real Life

Cyclists utilize each other’s slipstream in order to reduce the overall drag on the system and hence reduce the physical exertion.

Various models of slipstreaming are followed by cyclist for better performance.

Utilization of slipstreaming effect can be crucial factor in any speed races.

This method of drag reduction is effective only when high speed travelling is considered on highways which will improve the trailing vehicle’s performance. The flow around wake of an automobile is an interesting phenomenon and many experiments and analysis were conducted in favor of this.

CHAPTER TWO

Basic Definitions related to slipstreaming

A slipstream is a region behind a moving object in which a wake of fluid is moving at velocities comparable to the moving object, relative to the ambient fluid through which the object is moving.

Drafting or slipstreaming is a technique where two vehicles or other moving objects are caused to align in a close group reducing the overall effect of drag due to exploiting the lead object's slipstream.

Free stream velocity is the velocity of air far upstream of the object.

Relative wind: The direction of air is defined as relative wind.

Drag is the force that opposes a car's motion through the air. Drag is produced by every part of the vehicles. Drag is a mechanical force. It is generated by the interaction and contact of a solid body with a fluid (liquid or gas). It is not generated by a force field, in the sense of a gravitational field or an electromagnetic field. In gravitational field or an electromagnetic field one object can affect another object without being in actual or real contact. For drag to be produced, the solid body must be in contact with the fluid

A tubular chamber or structure in which a steady current of air can bemaintained at a controlled velocity, equipped with devices formeasuring and recording forces and moments on scale models is termed as a wind tunnel.

Critical distance is the minimum distance which must be maintained between vehicles while running in order to avoid accident.

Torque is the ability of the engine to do work (remember from physics that work is force x distance)

Horsepower or power is the rate at which a engine can do work (power is the rate of work, over time).

Proposal for Slipstreaming Effect Investigation

In order to investigate the effect of slipstreaming author have performed an experiment.For experimental purpose two models were made. A small sized model is always appropriate to examine the aerodynamic characteristics of different vehicles. So small sized models were made using wood .If someone wish to test the characteristics of a large model, a large scale wind tunnel facility is necessary for testing .For testing the model was placed in the middle of the test section supported by iron screw. For the purpose of measuring the surface pressure a box consists of the sensors was placed outside of the wind tunnel test section. Models were drilled through small diameter holes and small sizes tubes are placed inside the drilled holes. Tubes having small diameter were used to connect between the tubes inside the model and the sensors of the lab measurement system. By this measurement system surface pressure of the model at different points can be measured. Two types of models were prepared shown in figure One is (a) Semi-trailer truck and another one is (b) Sedan car model .Both models are prepared by wood. The semi-trailer truck has a length of 380mm, width of 86 mm and height of 106mm.The constructed sedan car has a length of 125 mm, width of 50 mm and height of 4 mm[1].

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Figure: Slipstreaming effect investigation procedure [1].

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Figure: Prepared model of truck [1].

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Figure: Prepared model of car [1].

For details of the experiment please read the following reference journal paper

Rubiat Mustak, Md.Habib Ullah Khan, Md.Mahbubur Rahman, Mohammad Mashud,“ Investigation of Slipstreaming Effect between a Semi trailer-truck and a Sedan Car ”, International Journal of Scientific & Engineering Research(IJSER), Volume 8, Issue 2,Pages PP.676-678,February-2017.

Author have a unique proposal for the reader of this book that they can examine slipstreaming effect by constructing different types of car models and made a possible combination of these cars that will be effective in reducing power needed to drive a car thus in turn reduces fuel consumption. As an example here is a photo graph of another constructed model of a long wheel base vehicle is shown. Several possible combinations of testing can be possible. Such as

1. Semi trailer truck and long wheel base car
2. Sedan car and long wheel base car.

Depending on the available facilities other models of cars can be constructed for possible combination of study.

illustration not visible in this excerpt

Figure: Constructed model a of long wheel base car [Note: This image is created by author himself].

CHAPTER THREE

The End:

Based on the investigation it was found that slipstreaming is effective at higher velocities of the vehicles. Though the mentioned investigation was performed between two specific vehicles. The investigation can also be performed using several other combinations of vehicles.Each time there will be different optimum or critical slipstreaming distance for different combinations.So further investigation in the same procedure is suggested.

References:

Bibliographies:

[1] M Bjerling, (2011)“Large Eddy Simulations on a Vehicle Platoon During In- Line Oscillations”, Bachelor’s thesis 2011:37, Chalmers University Of Technology Gothenburg, Sweden 2011.

[2] Ahmed S.R., (1981), “Wake structure of typical automobile shapes”, Trans. ASME, J. Fluids Eng. 103, 162-169.

[3] K. Stark “Slipstreaming Reduces Drag in Horse Racing up to 66 Percent”, Canadian Horse Journal, June 2015 issue.

[...]

^[1] Rubiat Mustak, Md.Habib Ullah Khan, Md.Mahbubur Rahman, Mohammad Mashud,“ Investigation of Slipstreaming Effect between a Semi trailer-truck and a Sedan Car ”, International Journal of Scientific & Engineering Research(IJSER), Volume 8, Issue 2,Pages PP.676-678,February-2017.

^[2] Shahrin H.A et al., (2010) “Numerical Analysis on the Effects of Air Flow in the Wake of a Large Vehicle on Trailing a Passenger Car”, Proceedings of MUCET 2010.